Islet glycolysis plays an important role in the regulation of glucose-stimulated insulhi release. Regulation of islet glycolysis is complicated by the dual glucose phosphorylation system : glucokinase and hexokinase. Glucokinase activity depends mostly on the level of the substrates. On the other hand, hexokinase activity is controlled by the activity of phosphofructokinase through the level of glucose 6-phosphate. Recently, glucose-stimulated insulin release was reported to be impaired in NIDDM. Glucagon-. or arginine-stimulated insulin release does not. These observations indicates that islet glycolytic system, which is proposed to regulate insulin release, may be impaired. In this study, we aimed to study. the alteration of islet glycolysis. -First, we prepared the cDNA probe of liver type phosphofructokinase. Using this probe and the cDNA probe of muscle type phosphofructokinase, we analyzed tissue distribution of these two types of phosphofructokinase. Using Northern analysis and
… MorePCR technique, most tissue including cultured b cells expressed both types of phosphofructokinase mRNA. Then, we analyzed muscle phosphofructokinase gene. It spans about 30kb, and has 24 exons. Its gene contains at least two premotor regions, facilitating the expression of the heterogeneous gene transcripts in tissue specific manner. Next, we analyzed the alteration of expression of glucokinase, phosphofructokinase, and pyruvate kinase mRNA in the rat liver. Rat liver contains glucokinase and liver type phosphofrutokinase as b cells do. Fasting decreased glucokinase mRNA level and refeeding restored its level quite rapidly. mRNA level of pyruvate kinase was also decreased after fasting. Its restoration by refeeding was slow. On the contrary to these two enzymes, mRNA level of phosphofructokinase was not altered either by fasting or by refeeding. Then, we studied the effect of insulin in the streptozotocin-treated diabetic rats. The effect of diabetic state and of the insulin treatment was resembled to that of fasting-refeeding. The increase in glucokinase mRNA after insulin injection was rapid. The restoration in pyruvate kinase mRNA was slow. Phosphofructokinase mRNA was not altered in these treatment. As shown in this study, the regulation of these enzymes were quite different. Less